This invention relates to a method for efficiently and uniformly applying refractory material onto eroded portions of the inner surface of a tap hole of a converter.
Conventionally, in tapping molten steel from a converter, the inner surface of the tap hole of the converter gradually erodes due to the molten steel and widens the bore or the inner diameter thereof. Such widening of the bore eventually shortens the time necessary for tapping and causes the splash of molten steel as well as the inclusion of slag into the tapped molten steel, whereby the thus produced steel cannot have uniform quality.
Accordingly, for assuring that the tapping time is kept within an allowable range, in one method, a refractory material carried on an elongated spoon-shaped trowel is manually applied onto the interior of the tap hole after each tapping operation for narrowing the bore of the eroded tap hole.
In the second method, tapping operations are consecutively repeated until the tapping time reaches the allowable limit. Subsequently, the eroded tap hole is smoothed by removing the eroded portion of the refractory material and the slag adhered thereto. A sleeve-shaped tap hole brick is inserted into the smoothed eroded tap hole, and finally refractory material is sprayed or cast into the annular space formed by the sleeve-shaped tap hole brick and the interior of the smoothed eroded tap hole.
In the above two methods, however, the repairing operation must be conducted in a critical condition at a location adjacent to the converter under high temperature. Accordingly, the improvement of such operations has been greatly demanded.
Besides the above-mentioned repairing methods, a method in which the refractory material is sprayed onto the interior of the tap hole has been partially conducted. In this method, however, when the refractory material layer applied onto the interior of the tap hole becomes slightly thicker than the optimal value, such layer tends to peel off and furthermore cannot provide a uniform diameter throughout the tap hole from the tap opening to the innermost end of the tap hole. Accordingly, in the tapping operation, molten steel does not flow out smoothly and a portion of the molten steel splashes, whereby the thus tapped steel deteriorates in quality thereof. Furthermore, the refractory material applied onto the tap hole by spraying shows high porosity and low strength so that it is extremely difficult to prevent the rapid widening of the tap hole as well as the rapid peeling off of the sprayed refractory material. Accordingly, a spraying operation must be conducted after every one or two tapping operations. Still furthermore, since the spray nozzle is subject to the high temperature within the tap hole, the refractory material within the spray nozzle tends to harden so that the spray outlet is clogged and further spraying may become impossible.
Still another repairing method is disclosed in Japanese laid-open patent application SHO52-17703.
In this method, a reciprocable rod extendably passes through an injection pipe and a plurality of umbrella-shaped members attached to the front extremity of the reciprocable rod opens like an umbrella to seal the innermost end of the tap hole and subsequently a refractory material charged into the injection pipe from the tapping outlet of the tap hole is applied onto the interior of the tap hole through a plurality of apertures formed on the entire surface of the injection pipe.
In this method, however, the injection pipe must be always filled with refractory material to uniformly inject the refractory material from all the apertures formed on the injection pipe. Otherwise, namely, when the injection pipe accommodates an insufficient amount of the refractory material, the above-mentioned uniform injection covering the entire length of the injection pipe becomes impossible, thereby the thus repaired interior of the tap hole shows unfavorable properties. Furthermore, the above method generally retains some amount of refractory material within the injection pipe after the tapping operation is over. Refractory material must be removed from the injection pipe and the removal of such material is, in general, troublesome. On the other hand, if the refractory material is left within the injection pipe, the material within the injection pipe and the supply hose tends to harden.
Furthermore, this method mainly uses the slurry-like refractory material which has a high fluidity because when the refractory material is of high viscosity and low fluidity, the supply of refractory material under pressure through a long hose becomes extremely difficult. Accordingly, in the operation, the injection pipe must be withdrawn from the sealed tap outlet of the tap hole after the refractory material becomes completely hardened. However, when the injection pipe is withdrawn well before the predetermined time, the refractory material applied onto the interior of the tap hole cannot maintain the applied shape thereof and flows out. When the applied refractory material is in a semi-solid state, such material may peel off. Even if such peeling-off does not take place, since the semi-solid material still has a relatively high fluidity, the water or the binder which attributes the fluidity to the refractory material is vaporized so that the refractory material applied on the interior of the tap hole shows the coarse internal structure and thereby has low strength and a short lifetime.
Furthermore, such semi-solid material cannot provide a uniform inner diameter and smooth surface through the entire length of the tap hole.
Furthermore, in the above repairing method, the injection pipe is withdrawn after the applied refractory material is sufficiently hardened. However, since the applied refractory material adjacent to the discharge apertures of the injection pipe is simultaneously hardened along with the refractory material located within and close to the discharge apertures, the withdrawal of the injection pipe causes a shearing force to the internal surface of the tap hole, whereby the inner surface of the applied refractory material may peel off. Furthermore, since the refractory material within the injection pipe is also hardened, the disposal of the refractory material is extremely difficult.
It is an object of the present invention to provide a method for repairing the tap hole of a converter furnace which can resolve the afore-mentioned defects of the conventional methods, and thereby can prolong the life-span of the tap hole of the converter.
This invention substantially provides a method for repairing the tap hole of a converter under high temperatures which is substantially conducted as follows.
(i) An injection pipe for applying refractory material onto the inner surface of the tap hole has its entire length enclosed by a porous cylindrical mold.
(ii) The injection pipe is inserted into the tap hole while being cooled by a coolant such as water.
(iii) The refractory material within the injection pipe is discharged from an opening formed at the front portion of the injection pipe through apertures of the perforated mold sleeve onto the inner surface of the tap hole.
Due to the above method, the thus applied refractory material can show the improved adhesion rate and properties.
This invention also provides for efficiently conducting the above repairing methods.